1. Field
The present invention relates to a pixel and an organic light emitting display device using the same.
2. Discussion of Related Art
Recently, various flat panel display devices that are lighter in weight and smaller in volume than a cathode ray tube, have been developed. Among the flat panel display devices, there are liquid crystal display devices, field emission display devices, plasma display panels, and organic light emitting display devices, etc.
Among the flat panel display devices, the organic light emitting display devices display images using organic light emitting diodes that generate light by a recombination of electrons and holes. Organic light emitting display devices are driven at low power consumption, with rapid response speed.
FIG. 1 is a schematic circuit diagram showing a pixel of a conventional organic light emitting display device.
Referring to FIG. 1, the pixel 4 of the conventional organic light emitting display device includes an organic light emitting diode OLED, and a pixel circuit 2 that is coupled to a data line Dm and a scan line Sn to control the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and the cathode electrode of the organic light emitting diode OLED is coupled to a second power supply ELVSS. The pixel circuit 2 controls the amount of current supplied to the organic light emitting diode OLED according to the data signal supplied to the data line Dm when a scan signal supplied to the scan line Sn. To this end, the pixel circuit 2 includes a second transistor M2 coupled between a first power supply ELVDD and the organic light emitting diode OLED, a first transistor M1 coupled between the second transistor M2, the data line Dm, and the scan line Sn, and a storage capacitor Cst that is coupled between the gate electrode and a first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and a first electrode of the first transistor M1 is coupled to the data line Dm. A second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. Here, the first electrode of the first transistor M1 is either a source electrode or a drain electrode, and the second electrode is an electrode other than the electrode of the first electrode. For example, if the first electrode is the source electrode, the second electrode is the drain electrode. When the scan signal is supplied to the scan line Sn, the first transistor M1 coupled between the scan line Sn and the data line Dm is turned on to supply the data signal supplied from the data line Dm to the storage capacitor Cst. Thus, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and the first electrode is coupled to the other terminal of the storage capacitor Cst and the first power supply ELVDD. The second electrode of the second transistor M2 is coupled to the anode electrode of the organic light emitting diode OLED. The second transistor M2 controls the amount of current flowing from the first power supply ELVDD to the second power supply ELVSS via the organic light emitting diode OLED in accordance with the voltage stored in the storage capacitor Cst. Accordingly, the organic light emitting diode OLED generates light corresponding to the amount of current supplied by the second transistor M2.
However, an issue with the conventional organic light emitting display device as described above is that an image having a desired brightness cannot be displayed due to changes in efficiency according to the deterioration of the organic light emitting diode OLED. That is, the organic light emitting diode OLED deteriorates as time elapses, and accordingly, light having a gradually lowering brightness is generated corresponding to the same data signal. Another issue with the conventional organic light emitting display device is that an image having a uniform brightness cannot be displayed due to the non-uniformity in threshold voltage/mobility of the driving transistors M2 included in each pixel 4.